1. Industrial Field of the Invention
The present invention relates to a fuel tank structure using a fuel cutoff valve with a float.
2. Description of Related Art
A conventional fuel tank to be installed in an automobile includes a recessed portion 1a formed at the central portion on a top wall of the tank 1, the shape of the recessed portion being adapted corresponding to a certain component surrounding the fuel tank, and two air chambers, i.e., a first air chamber 2 and a second air chamber 3 separate from each other, as shown in FIG. 6. The air chambers are formed on both sides of the recessed portion 1a. The both air chambers 2 and 3 have top walls positioned at levels in height different from each other.
Fuel cutoff valves 4 and 5 are projectingly provided on the top walls of both the air chambers 2 and 3. The fuel cutoff valves 4 and 5 operate to discharge fuel evaporation gas in the air chambers 2 and 3 and to interrupt fuel from flowing out of the fuel tank when a level of the fuel is raised to exceed a predetermined height.
Typically, such a fuel cutoff valve has a structure as illustrated in FIG. 7. More specifically, discharge holes 7 for the fuel evaporation gas are formed at an upper end of a casing 6 so that the fuel evaporation gas generated in the air chamber is exhausted from the discharge holes 7 through a valve seat opening 8, a passage 9 and a check valve 40 to a canister (not shown).
When the fuel level is raised up to the casing 6 and a float valve 10 is sunk in the fuel, the float valve 10 rises due to its buoyancy so that its valve portion 10a closes the valve seat 8 to thereby prevent the fuel from flowing out through the passage 9 to the canister.
When the fuel is supplied into the fuel tank 1, the level of the fuel is stopped at a position of an inner edge of a breather pipe 12 by means of the check valve 40 under a condition in which the tank is fully filled with the fuel supplied through the fuel tube 11 shown in FIG. 6. For the reasons, in the fuel tank having the above-mentioned air chambers 2, 3 with the top walls having the different heights from each other, under the condition in which the fuel tank is fully filled with the fuel as shown in FIG. 6, a distance H from the fuel level to the top wall in the first air chamber 2 having the high-level top wall is relatively long. A distance L from the fuel level to the top wall in the second air chamber 3 having the low-level top wall is relatively short.
Consequently, in the conventional fuel tank including the fuel cutoff valves 4 and 5 having heights equal to each other, in some cases, the fuel level comes close to the fuel cutoff valve 5, or the fuel cutoff valve 5 is sunk in the fuel in the second air chamber 3 under the condition in which the tank is fully filled with the fuel.
Under such a condition, when the automobile is turned or braked, the fuel in the fuel tank quakes so that waves of the fuel are splashed on the fuel cutoff valve 5. Part of the fuel waves sometimes enters an upper chamber of the float valve 10 from the discharge holes 7 for the fuel evaporation gas formed at the upper end of the casing 6. Because pressure in the air chamber 3 is higher than an atmospheric pressure on the side of the canister, the fuel spouts from the valve seat opening 8 due to the pressure difference between the air chamber 3 and the canister so as to flow through the passage 9 into the canister,
Thus, the prior art possesses a problem in that deterioration of the canister is accelerated in the case where the fuel flows into the canister.